首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   27755篇
  免费   1245篇
  国内免费   325篇
电工技术   511篇
综合类   565篇
化学工业   4870篇
金属工艺   635篇
机械仪表   968篇
建筑科学   935篇
矿业工程   190篇
能源动力   745篇
轻工业   2369篇
水利工程   250篇
石油天然气   184篇
武器工业   31篇
无线电   3156篇
一般工业技术   3860篇
冶金工业   6582篇
原子能技术   230篇
自动化技术   3244篇
  2023年   150篇
  2022年   395篇
  2021年   551篇
  2020年   361篇
  2019年   467篇
  2018年   531篇
  2017年   490篇
  2016年   594篇
  2015年   504篇
  2014年   743篇
  2013年   1313篇
  2012年   1074篇
  2011年   1350篇
  2010年   1026篇
  2009年   1102篇
  2008年   1069篇
  2007年   1033篇
  2006年   870篇
  2005年   755篇
  2004年   804篇
  2003年   1036篇
  2002年   1297篇
  2001年   1101篇
  2000年   671篇
  1999年   695篇
  1998年   2204篇
  1997年   1397篇
  1996年   960篇
  1995年   639篇
  1994年   486篇
  1993年   553篇
  1992年   224篇
  1991年   220篇
  1990年   204篇
  1989年   179篇
  1988年   178篇
  1987年   143篇
  1986年   154篇
  1985年   178篇
  1984年   91篇
  1983年   106篇
  1982年   96篇
  1981年   132篇
  1980年   126篇
  1979年   64篇
  1978年   67篇
  1977年   200篇
  1976年   369篇
  1975年   63篇
  1973年   55篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
A patient who developed a mixed neuroendocrine carcinoma and adenocarcinoma at the site of a previous long-standing ileostomy is reported. The neuroendocrine features are documented by both ultrastructural and immunocytochemical findings. Carcinoma arising in an ileostomy site is rare but has been recorded in patients with long-standing ileostomies after colectomy for chronic inflammatory bowel disease, as in this patient. Neuroendocrine carcinoma developing in this setting apparently has not been described before, however.  相似文献   
92.
The basis of protein stability has been investigated by the structural comparison of themophilic enzymes with their mesophilic counterparts. A number of characteristics have been found that can contribute to the stabilization of thermophilic proteins, but no one is uniquely capable of imparting thermostability. The crystal structure of 3-isopropylmalate dehydrogenase (IPMDH) from the mesophiles Escherichia coli and Salmonella typhimurium have been determined by the method of molecular replacement using the known structure of the homologous Thermus thermophilus enzyme. The structure of the E. coli enzyme was refined at a resolution of 2.1 A to an R-factor of 17.3%, that of the S. typhimurium enzyme at 1.7 A resolution to an R-factor of 19.8%. The three structures were compared to elucidate the basis of the higher thermostability of the T. thermophilus enzyme. A mutant that created a cavity in the hydrophobic core of the thermophilic enzyme was designed to investigate the importance of packing density for thermostability. The structure of this mutant was analyzed. The main stabilizing features in the thermophilic enzyme are an increased number of salt bridges, additional hydrogen bonds, a proportionately larger and more hydrophobic subunit interface, shortened N and C termini and a larger number of proline residues. The mutation in the hydrophobic core of T. thermophilus IPMDH resulted in a cavity of 32 A3, but no significant effect on the activity and thermostability of the mutant was observed.  相似文献   
93.
This paper analyses the determination of visibility of journals in which researchers of INRA (National Institute for Agricultural Research) publish. The corpus is comprised of 671 articles published over a period of four years in 258 journals. The advantage of the method applied for determining the visibility of journals is that it combines two approaches: a) bibliometric indicators (coverage by the ISI-publications and by two specific French databases) and b) experts' opinions (10 economists and sociologists). The main results are: a) There is a convergence between the opinion of the experts and «visibility» in the databases, b) The impact factor confirms the main opinions of the experts. The first journals ranked by the experts and JCR Social Sciences are the same but represent only 40 per cent of the total journals analysed. The other journals were revealed by the experts and French databases.«Whoever seeks to pass a balanced but lucid judgement on the general trends of the activity carried out by the profession to which he belongs, is liable to say either banalities or to hurt his colleagues»The notion which we retain of core is that which is successively and conjointly validated by the experts and by the major databases representative of the field.This study was financed by the Department of Rural Economy and Sociology of INRA.  相似文献   
94.
Two real-time algorithms for active power measurements on Pulse Width Modulation (PWM) electric drives are proposed. The former is an off-line algorithm reducing truncation error through an accurate signal period estimation and a proper window. The second is an on-line algorithm based on a low-pass IIR digital filter with an optimized transient phase. Numerical results of the metrological characterization of such algorithms, aimed to suggest criteria for their use, are presented. The experimental results of tests carried out on an actual drive confirm numerical simulations and are in perfect agreement with those of a well-acclaimed algorithm  相似文献   
95.
96.
97.
Cystic fibrosis (CF) is the most common lethal autosomal recessive disorder among Caucasians and is caused by abnormalities in the cystic fibrosis transmembrane conductance regulator gene (CFTR). CFTR gene encodes a chloride channel that regulates secretion in many exocrine tissues especially pancreatic and pulmonary tissues. The clinical presentation of cystic fibrosis is highly variable with isolated CAVD (congenital absence of vas deferens) and/or typical pancreatic and pulmonary manifestations. Over 500 mutations in the CFTR gene have been described and vary among different geographic locations. The severity of clinical manifestations and specially the pulmonary disease is poorly correlated with genotype. It is interesting to collect clinical and genetical data by analysing a larger cohort of CF patients. These results are likely to improve our understanding of the physiopathology of CF and the genetic counselling; particular biochemical defect could lead to more specific treatments in the future. From our 110 patients selected in Champagne-Ardenne country, we analysed the entire coding sequence of CFTR gene and detected 95% of CF mutations and in fact, 89.5% if we include the CAVD patients; 59.4% of CF mutations were detected for these patients. Three new mutations have been here reported. We found numerous CF mutations with a large distribution throughout the gene. Nevertheless, three exons are mainly involved: 10, 11 and 21. Relationships between the genotype and phenotype are difficult to assess.  相似文献   
98.
99.
100.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号